Heat Exchanger Arrangement

ABSTRACT

A refrigeration system includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the first heat exchanger is positioned within a housing which defines a flow path for heat exchange fluid and the housing defines a zone of reduced flow area along the flow path, and wherein the first heat exchanger is positioned in the zone of reduced flow area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This applications claims the benefit of the filing date of earlier filedprovisional application Ser. No. 60/663,962 filed Mar. 18, 2005.Further, copending application docket 05-258-WO, entitled HIGH SIDEPRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filedon even date herewith, and the aforesaid provisional application Ser.No. 60/663,962, disclose prior art and inventive cooler systems. Thedisclosure of said applications is incorporated by reference herein asif set forth at length.

BACKGROUND OF THE INVENTION

The invention relates to a heat exchanger arrangement for a vaporcompression system, especially a transcritical vapor compression system.

The heat rejection process in transcritical vapor compressionrefrigeration applications and systems occurs at a pressure above thecritical pressure of the refrigerant. The refrigerant does not undergo aphase change during this process and the temperature of the refrigerantchanges throughout the entire heat rejection process. The energyefficiency of the refrigeration system increases if the heat exchangerarrangement approaches an ideal counter flow arrangement with the heatsink.

It is therefore a primary object of the invention to provide a systemhaving an efficient heat exchanger arrangement.

It is a further object of the invention to provide such a system whichis readily incorporated into existing refrigeration systems.

Other objects and advantages will appear herein.

SUMMARY OF THE INVENTION

According to the invention, the foregoing objects and advantages havebeen attained.

According to the invention, a refrigeration system is provided whichcomprises a compressor for driving a refrigerant along a flow path in atleast a first mode of system operation; a first heat exchanger along theflow path downstream of the compressor in the first mode; a second heatexchanger along the flow path upstream of the compressor in the firstmode; and a pressure regulator or expansion device in the flow pathdownstream of the first heat exchanger and upstream of the second heatexchanger in the first mode, wherein the first heat exchanger ispositioned within a housing which defines a flow path for heat exchangefluid and the housing defines a zone of reduced flow area along the flowpath, and wherein the first heat exchanger is positioned in the zone ofreduced flow area.

According to the invention, a refrigeration system is provided whichincludes a compressor for driving a refrigerant along a flow path in atleast a first mode of system operation; a first heat exchanger along theflow path downstream of the compressor in the first mode; a second heatexchanger along the flow path upstream of the compressor in the firstmode; and a pressure regulator or expansion device in the flow pathdownstream of the first heat exchanger and upstream of the second heatexchanger in the first mode, wherein the first heat exchanger comprisesa plurality of substantially parallel refrigerant flow paths, andwherein heat exchange fluid for the first heat exchanger is directed incounter flow substantially transverse to the refrigerant flow paths.

A preferred embodiment is drawn to transcritical vapor compressionoperation using CO₂ refrigerant fluid. Serpentine and/or parallelmodular refrigerant flow paths are provided. A particular environment ofuse for the invention is in connection with so-called bottle coolers, orcooling units for cooling and storing beverages. Such coolers can be inthe form of vending machines are refrigerator cases, for example.

In one embodiment, the housing of the beverage cooler defines aninternal flow area for heat exchange fluid such as air, and this flowarea has a flow restriction which serves to speed flow of the heatexchange fluid therethrough. According to the invention, the refrigerantflow paths are positioned at the flow restriction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a counter flow heat exchangerarrangement according to the invention;

FIG. 2 is a schematic illustration of an alternate counter flow heatexchanger arrangement according to the invention;

FIG. 3 is an illustration of a preferred structure for a beverage coolerincluding the heat exchanger arrangement of the present invention;

FIG. 4 illustrates a preferred type of heat exchanger according to theinvention; and

FIG. 5 illustrates a preferred embodiment of the structure shown in FIG.3.

DETAILED DESCRIPTION

The invention relates to refrigeration systems and, more particularly,to systems operating in a transcritical vapor compression regime, oneparticular embodiment of which is a beverage cooler. According to thisinvention, a heat exchanger configuration is utilized which providesefficient exchange of heat between a refrigerant fluid and a heatexchange fluid.

A transcritical vapor compression system operates at pressures above thecritical pressure of the refrigerant and, therefore, the refrigerantdoes not undergo a phase change during the process. Under thesecircumstances, it has been found that a counter flow arrangement of theheat rejection heat exchanger with respect to the heat exchange fluidprovides better efficiency in operation, and this counter flowarrangement can be approached by a heat exchanger consisting of a singleflow path of several parallel flow path segments.

It has also been found that the position of a heat exchanger within thehousing is important, and positioning of a heat exchanger in an area ofincreased flow velocity has been found to make the heat exchange processmore efficient.

FIG. 1 shows a refrigerant system 10 having a compressor 12, a firstheat exchanger 14, a second heat exchanger 16, an expansion device 18and refrigerant lines connecting these components in serial fashion asillustrated.

FIG. 3 further illustrates a beverage cooler 20 into which system 10 ispositioned. FIG. 3 shows compressor 12 as well as first heat exchanger14 and second heat exchanger 16. Cooler 20 has a housing which defines afirst heat exchange fluid flow path (arrows 22) wherein external air isdrawn from an inlet 24, past first heat exchanger 14, and to an outlet26. A second fluid flow path (arrows 28) is also defined, and passesfrom within the space of the beverage cooler, past second heat exchanger16, and back to the refrigerated space. As shown in FIG. 3, flow path 22passes through the housing and passes through a zone 23 of reduced flowarea. At zone 23, air flowing through the housing increases in velocity.According to the invention, it is preferred to position heat exchanger14 at zone 23.

FIG. 1 shows a simplified configuration of first heat exchanger 14 inaccordance with the invention, and shows the heat exchanger in the formof a single refrigerant flow path or tube formed into a series ofsubstantially parallel flow path segments. In this embodiment, thesegments are serially fed with refrigerant fluid from compressor 12 suchthat the flow path segments include an upstream flow path segment 30 anda downstream flow path segment 32. In the embodiment shown in FIG. 1,all flow path segments are part of a single serpentine path and, thus,each segment is progressively further downstream as it relates to flowof refrigerant, when considered from upstream segment 30 to downstreamsegment 32. First heat exchanger 14 is positioned within the housing ofbeverage cooler 20 such that incoming heat exchange fluid 22 firstpasses the downstream refrigerant flow path segment 32, and then passedincreasingly over the next flow path segments in order until finallypassing upstream flow path 30. This configuration has been found,according to the invention, to provide for good heat exchange betweenthe heat exchange fluid and the refrigerant. particularly when thesystem defined is a transcritical vapor compression system.

FIG. 2 shows an alternative embodiment wherein the flow path segmentsare broken up into two main groups or components of the heat exchanger,and wherein the groups are positioned so as to define an upstream and adownstream component. Within each component, segments are defined inparallel. Incoming heat exchange fluid, as shown, passes first over thedownstream component and then over the upstream component.

It should be appreciated that the configurations of FIGS. 1 and 2 areexamples of the counter flow arrangement of the present invention, andthat alterations to these specific structures could of course be made bya person of skill in the art, well within the broad scope of the presentinvention. Further, one preferred embodiment of a heat exchanger for usein accordance with the invention is a wire-on-tube heat exchanger, anexample of which is illustrated in FIG. 4. FIG. 4 shows a portion of aheat exchanger 50 defined by a single flow tube 52 which has aserpentine flow configuration as illustrated in FIG. 1 and which also isconfigured to have a vertical structure as well. Specifically, heatexchanger 50 is shaped to have alternating angled sections 54, 56 whenconsidered in the direction of air flow as shown by arrow 58. A seriesof wires 60 are positioned along heat exchanger 50 in a substantiallytransverse direction to the paths defined by tube 52, and wires 60preferably follow tube 52 along the sections 54, 56. Wires 60 canadvantageously be positioned on both sides of tube 52 as shown in FIG.4. FIG. 4 illustrates several turns of a wire-on-tube heat exchanger. Itshould be appreciated that the actual heat exchanger could continue forone or more additional angled sections 54, 56, to provide for thedesired flow length of the heat exchanger.

As set forth above, FIG. 3 shows a further embodiment of the presentinvention wherein system 10 is incorporated into a beverage cooler 20.In this system, the beverages would be stored in a refrigerated areapositioned above the portion illustrated, and communicated with the flowof air along path 28.

Flow path 22 represents flow of outside or ambient air which entersthrough an inlet 24 located at the front 34 of cooler 20 and passes afirst component 14 a of first heat exchanger 14 and then a secondcomponent 14 b of first heat exchanger 14, and then to an outlet 26preferably at the rear 36 of cooler 20.

An inner housing wall 38 separates the area of flow path 22 from thearea of flow path 28. This wall also serves to define a zone along flowpath 22 where the cross sectional area, or flow area, is constricted.This reduction in flow area along path 22 serves to increase thevelocity of flow through same. For this reason, second component 14 b offirst heat exchanger 14 is preferably positioned at the zone ofrestricted flow as shown so that the increased flow velocity of heatexchange fluid passes over this heat exchanger. It has been found,according to the invention, that this positioning helps to furtherincrease the efficiency in heat exchange between the heat exchange fluidand the refrigerant. Reduced flow area zone 23 is in this embodimentshown toward the rear of path 22, and is substantially completely filledwith heat exchanger component 14 b.

In further accordance with the invention, and as shown in FIG. 5, a heatexchanger such as the wire-on-tube heat exchanger of FIG. 4 canadvantageously be positioned at the zone 23 of increased flow velocity,and this heat exchanger is particularly efficient in exchanging heatwith the flow of air passing through zone 23. In this configuration, itis possible to completely eliminate the heat exchanger from the locationoccupied by heat exchanger 14 a in FIG. 3, and thereby provide thisspace for other uses. Thus, in one aspect of the present invention, aheat exchanger is advantageously positioned within the housing at a zone23 where there is a decreased air flow area and a resulting increase inair flow velocity, and it is further preferred to position a wire ontube heat exchanger in zone 23. As used herein, a wire-on-tube heatexchanger is considered to be a heat exchanger defined by one or moretubes, preferably a single tube, which has wires positioned forinteraction with a passing air flow to increase heat exchangeefficiency. Such a heat exchanger is particularly desirable forpositioning in a zone such as zone 23 since most heat exchangers wouldhave too great of a resistance to air flow to position in such alocation. However, a wire-on-tube heat exchanger has sufficiently lowresistance to air flow that positioning of such a heat exchanger in zone23 does not significantly interfere with the flow dynamics of thesystem, and further the wire-on-tube heat exchanger is particularlyefficient at heat exchange under such flow conditions.

As set forth above, FIG. 3 shows one embodiment of structure used togenerate flow along paths 22 and path 28. Flow along flow path 22 can begenerated using a fan 40 driven by a motor 42 as shown. In similarfashion, flow along path 28 can be generated by a fan 44 driven by amotor 46 as shown. Other structures for generating the desired flowswould be well known to a person of skill in the art and are well withinthe scope of the present invention.

It should be appreciated that the refrigerant flow paths represented byfirst heat exchanger 14 and its components 14 a, 14 b, can be formed astubes, micro-channels or mini-channels, or the like. The secondary fluidsurface area of the tube can be increased, for example with finsattached to the tube. The fins can be of any type, and can be in theshape of plates, wires, louvered fins or any other shape. One preferredembodiment is that referred to as a “wire-on-tube” configuration asdescribed above and illustrated in FIG. 4.

In bottle cooler applications and other small refrigeration applicationswith carbon dioxide (CO₂) as refrigerant this invention offersparticular benefits. This invention allows utilizing the space in avolume available for the heat exchanger most effectively. Additionally,the high operating pressure of CO₂ refrigeration applications reducesthe effect of pressure drop on the system performance. Therefore, thehigh pressure drop in a single-tube serpentine arrangement of the heatexchanger as shown in FIG. 1 does not reduce the system performancesignificantly, while the effective utilization of the volume availablefor the heat exchanger paths maximizes the system performance.Specifically, the volume normally occupied by a heat exchanger 14 a(FIG. 3) can be utilized for other system components, or to makeexisting components larger and/or more efficient.

The system according to the invention is discussed herein in terms ofhaving upstream and downstream relationship with various components ofthe refrigerant circuit in at least one mode of operation. This takesinto account that a device such as a beverage cooler utilizing theapparatus of the present invention could have more than one mode ofoperation, and/or intermittent modes of operation, aside from the“normal” cooling mode wherein the first heat exchanger gives off heatand the second heat exchanger cools air within a refrigerated space.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, when implemented as a remanufacturing of an existing system orreengineering of an existing system configuration, details of theexisting configuration may influence details of the implementation.Accordingly, other embodiments are within the scope of the followingclaims.

1. A refrigeration system comprising: a compressor for driving arefrigerant along a flow path in at least a first mode of systemoperation; a first heat exchanger along the flow path downstream of thecompressor in the first mode; a second heat exchanger along the flowpath upstream of the compressor in the first mode; and a pressureregulator or expansion device in the flow path downstream of the firstheat exchanger and upstream of the second heat exchanger in the firstmode, wherein the first heat exchanger is positioned within a housingwhich defines a flow path for heat exchange fluid and the housingdefines a zone of reduced flow area along the flow path, and wherein thefirst heat exchanger is positioned in the zone of reduced flow area. 2.The system of claim 1, wherein the first heat exchanger comprises awire-on-tube heat exchanger.
 3. The system of claim 1, wherein the heatexchanger comprises a plurality of substantially parallel refrigerantflow path segments, and wherein the heat exchange fluid is directed incounter flow with respect to refrigerant in the first heat exchanger,and substantially transverse to the refrigerant flow path segments.
 4. Arefrigeration system comprising: a compressor for driving a refrigerantalong a flow path in at least a first mode of system operation; a firstheat exchanger along the flow path downstream of the compressor in thefirst mode; a second heat exchanger along the flow path upstream of thecompressor in the first mode; and a pressure regulator or expansiondevice in the flow path downstream of the first heat exchanger andupstream of the second heat exchanger in the first mode, wherein thefirst heat exchanger comprises a plurality of substantially parallelrefrigerant flow path segments, and wherein heat exchange fluid for thefirst heat exchanger is directed in counter flow substantiallytransverse to the refrigerant flow path segments.
 5. The system of claim4 wherein the refrigerant flow paths have an upstream end and adownstream end with respect to refrigerant flow from the compressor, andwherein the heat exchange fluid is directed from the downstream end tothe upstream end of the refrigerant flow path segments to provide thecounter flow.
 6. The system of claim 4, further comprising structure forguiding flow of the heat exchange fluid substantially transverse to therefrigerant flow path segments.
 7. The system of claim 4 wherein therefrigerant flow path segments are defined by at least one refrigerantflow path in a serpentine arrangement.
 8. The system of claim 4 whereinthe refrigerant flow path segments are defined by a plurality of heatexchange modules arranged in series with respect to refrigerant flow andin counter flow with the heat exchange fluid.
 9. The system of claim 8wherein each heat exchange module comprises a plurality of substantiallyparallel refrigerant flow path segments.
 10. The system of claim 4wherein: the refrigerant comprises, in major mass part, CO₂; and thefirst and second heat exchangers are refrigerant-air heat exchangers.11. The system of claim 4, wherein the system is adapted to operate in atranscritical vapor compression mode.
 12. A beverage cooling devicecomprising the system of claim
 4. 13. The device of claim 12, whereinthe beverage cooling device comprises a housing having an inlet and anoutlet for the heat exchange fluid, wherein the housing defines a flowrestriction between the inlet and the outlet, and wherein the first heatexchanger is positioned at the flow restriction.
 14. A method forexchanging heat between a refrigerant and a heat exchange fluid,comprising: operating a compressor to drive a refrigerant from thecompressor to a heat exchanger in a housing which defines a flow pathfor heat exchange medium, wherein the housing defines a zone ofdecreased flow area for the heat exchange medium, and wherein the heatexchanger is positioned in the zone; and passing a heat exchange fluidover the heat exchanger in the zone in a direction which issubstantially transverse to the substantially parallel flow paths. 15.The method of claim 14, wherein the heat exchanger comprises a pluralityof substantially parallel flow path segments.
 16. The method of claim15, further comprising feeding the substantially parallel flow pathsegments sequentially so as to define at least one upstream flow pathand at least one downstream flow path with respect to refrigerant flowfrom the compressor, and wherein the passing step comprises passing heatexchange fluid over the substantially parallel flow path segments fromthe downstream flow path to the upstream flow path.